Recently, an active matrix display device using active elements such as TFTs, notably a liquid crystal display device and an organic EL display device which are rapidly spreading as an alternative to a cathode-ray tube (CRT), is widely used in a television, a monitor, a mobile phone and the like, taking advantage of its characteristics such as energy saving, thin-typed, lightweight and the like.
In particular, some liquid crystal display devices integrated in medium and small electronic apparatuses such as mobile phones and notebook computers began to adopt a gate driver monolithic (GDM) technology using amorphous silicon in order to realize a reduction of manufacturing costs. The application of such a gate driver monolithic (GDM) technology is expanding from medium and small electronic apparatuses to large-scale apparatuses such as a television.
For example, Patent Literature 1 describes a substrate for a liquid crystal display device in which pixel transistors in a display region and various types of transistors in a gate driving circuit region are formed with amorphous silicon thin films.
In the display region of the substrate for a liquid crystal display device, a drain electrode of the pixel transistor and a pixel electrode are electrically connected via a contact hole formed on a passivation film. The display region thus has a structure in which the pixel electrode is provided on the passivation film, which is a so-called “Pixel on Passivation” structure. The pixel transistor is formed as a bottom-gate transistor.
Also the gate driving circuit region of the substrate for a liquid crystal display device, as illustrated in FIG. 13, has a structure in which an electrode 140 of a same layer as the pixel electrode is formed on a passivation film 180 in order to electrically connect a main wiring 150 to a branch wiring 160, which will be explained in detail later.
Patent Literature 1 teaches that the driving circuit and wirings thereof to be formed in the gate driving circuit region are produced simultaneously with the display region by using a five (or four) mask production process, which process is generally used for producing only the display region, so that the gate driving circuit region can be integrated onto the substrate without an additional process, thereby making it possible to lower the production cost.
The configuration of the gate driving circuit region of the substrate for a liquid crystal display device will be described below with reference to FIGS. 12 to 13.
FIG. 12 is a plane view illustrating the gate driving circuit region of the substrate for a liquid crystal display device.
As illustrated in FIG. 12, driving transistors for shift registers are formed in that portion of the gate driving circuit region (in the right edge in FIG. 12) which is proximal to a display region (not-illustrated). A wiring region where a plurality of the main wirings 150 for applying a signal to respective ones of the shift registers are formed is provided in a vicinity of that portion of the gate driving circuit region, which is located distally from the display region.
Further, control transistors are formed in a region between the wiring region and the region where the driving transistors are formed.
The branch wirings 160 which connect the main wiring 150 to the driving transistor and the control transistor of the respective shift registers are formed of a different layer from that of the main wirings 150. According to the configuration of Patent Literature 1, the main wirings 150 are formed of the same layer as gate wiring patterns (gate patterns), while the branch wirings 160 are formed of the same layer as data wiring patterns (data patterns).
FIG. 13 is a cross-sectional view taken along the line C-C′ in FIG. 12, illustrating a connection part of the main wiring 150 to the branch wiring 160.
As illustrated in FIG. 13, an insulating film 170 is provided between the main wiring 150 and the branch wiring 160, and the passivation film 180 is further provided so as to cover the branch wiring 160 and the insulating film 170.
A hole formed in the insulating film 170 and the passivation film 180 so as to partially uncover the main wiring 150 is defined as a first contact hole 190, and a hole formed in the passivation film 180 so as to partially uncover the branch wiring 160 is defined as a second contact hole 200.
As illustrated in FIG. 12, the main wirings 150 and the branch wirings 160 intersect in the wiring region, whereas they do not intersect in the connection part as illustrated in FIG. 13.
The main wiring 150 and the branch wiring 160 are electrically connected via an electrode 140 formed of the same layer as the pixel electrode being formed in the first contact hole 190 and the second contact hole 200.
Patent Literature 1 further teaches that it is preferable to reduce the line width of the branch wiring 160 which intersects the main wiring 150, in order to decrease capacitance of the main wiring 150.